This invention relates to the conversion of methane to higher hydrocarbons. A particular application of this invention is a method for converting natural gas to more readily transportable material.
Methane can be converted to higher hydrocarbons by reaction at conditions of elevated temperature - e.g. a temperature selected within the range from about 500.degree. C. to about 10000.degree. C. For example, methane can be contacted with an oxidative synthesizing agent at such elevated temperatures in order to produce higher hydrocarbons. Oxidative synthesizing agents are compositions having as a principal component at least one oxide of at least one metal which compositions produce C.sub.2 + hydrocarbon products, co-product water, and a composition comprising a reduced metal oxide when contacted with methane at synthesizing conditions. Reducible oxides of several metals have been identified which are capable of converting methane to higher hydrocarbons. In particular, oxides of manganese, tin, indium, germanium, lead, antimony, bismuth, praseodymium, terbium, cerium, iron and ruthernium are most useful. See commonly-assigned U.S. Pat. Nos. 4,443,644 (Sb); 4,443,649 (Mn); 4,444,984 (Sn); 4,445,648 (In); 4,443,645 (Ge); 4,443,674 (Pb); 4,443,646 (Bi); 4,499,323 (Pr); 4,499,324 (Ce); and 4,593,139 (Ru), the entire contents of which are incorporated herein by reference. See also commonly-assigned U.S. patent application Ser. No. 06/666,694 (Fe) the entire content of which is incorporated herein by reference.
Commonly-assigned U.S. Pat. No. 4,554,395 discloses and claims a process which comprises contacting methane with an oxidative synthesizing agent under elevated pressure (2-100 atmospheres) to produce greater amounts of C.sub.2 + hydrocarbon products.
Commonly-assigned U.S. Pat. No. 4,560,821 discloses and claims a process for the conversion of methane to higher hydrocarbons which comprises contacting methane with particles comprising an oxidative synthesizing agent which particles recirculate between two physically separate zones--a methane contact zone and an oxygen contact zone.
U.S. Pat. No. 4,499,322 discloses and claims a process for the conversion of methane to higher hydrocarbon and comprises contacting methane with a oxidative synthesizing agent containing a promoting amount of alkali metal and/or compounds thereof.
U.S. Pat. No. 4,495,374 discloses and claims a process for the conversion of methane to higher hydrocarbons which comprises contacting methane with an oxidative synthesizing agent containing a promoting amount of alkaline earth metal and/or compounds thereof.
Hinsen and Baerns report studies of a continuous mode for the oxidative coupling of methane wherein regeneration air is cofed with methane feed. Hinsen, W. and Baerns, M., "Oxidative Koppling von Methan zu C.sub.2 - Kohlenwasserstoffen in Gegenwart unterschiedlicher Katalsatoren", Chemiker-Zeitung, Vol. 107, No. 718, pp. 223-226 (1983). Using a catalyst based on lead oxide and gamma-alumina in a fixed bed reactor operated at 1 atmosphere total pressure and 600-750 degrees C. they report results of approximately 53% selectivity to ethane and ethylene at 8% methane conversion for a feed consisting of about 50% methane, 25% air and 25% nitrogen. Other metal oxides studied by Hinsen and Baerns included oxides of Bi, Sb, Sn and Mn.
U.S. Pat. No. 4,523,049, discloses and claims a process for converting methane to higher hydrocarbons which comprises contacting methane and an oxygen-containing gas with a solid comprising a reducible metal oxide and an alkali/alkaline earth metal promotor.
U.S. Pat. No. 4,523,050 discloses and claims a process for converting methane to higher hydrocarbons which comprises contacting methane and an oxygen-containing gas with a manganese silicate.
Commonly-assigned U.S. patent application Ser. No. 06/738,110, filed May 24, 1985, discloses and claims a method for converting methane to higher hydrocarbons wherein methane and a gaseous oxidant are contacted with a nonacidic solid. In a preferred embodiment, the solid comprises an alkali metal component associated with a support material. The application also teaches conducting the contacting in the presence of halogen promotors when employing alkali-promoted solids.
Commonly-assigned U.S. patent application Ser. No. 6/738,114, filed May 24, 1985, discloses and claims a process wherein methane and a gaseous oxidant are contacted with a nonacidic solid in the presence of halogen promotor but in the absence of an alkali metal promotor.
Commonly-assigned U.S. patent application Ser. No. 014,406 discloses and claims a method for converting methane to higher hydrocarbons wherein methane and added water are contacted in the substantial absence of added gaseous oxidant with a solid comprising at least one reducible metal oxide.
Commonly-assigned U.S. patent application Ser. No. 014,405 discloses and claims a method for converting methane to higher hydrocarbons wherein methane and a gaseous oxidant together with added water are contacted with a nonacidic solid and/or a reducible metal oxide.
The reaction products of the foregoing processes are hydrocarbons, carbon oxides, coke and water.
A problem in the past has been a decline in the activity of the solid contact materials, especially where alkali metals such as lithium form a component of the contact solid. Upon prolonged use at the reaction conditions necessary for methane conversion, activity of the contact solids tends to decline as manifested by lowered methane conversion until the activity becomes uneconomically low. Selectivity also declines.